The present invention relates in general to semiconductor devices and, more particularly, to low profile packaged semiconductor devices.
In semiconductor device manufacture, semiconductor dice are mounted within sealed packages. A non-conductive encapsulation surrounds the die providing protection from damage and contaminates. In addition, the package provides a lead system for connecting circuitry fabricated on the die to external circuitry, such as a printed circuit board.
A typical die has a back surface with one electrode or no circuitry, and a top surface having a component or integrated circuitry fabricated thereon. The component is electrically accessible via bond pads located on the outer portion of the top surface, which may be arranged in a wide variety of patterns both near the edge of the die and at the center of the die.
Often, the initial step in the packaging process is attaching a lead frame, made of metal sheet-stock, to the back surface of the die. A wire is ball bonded at one end to a bond pad, and the other end of the wire is stitch bonded to a lead of the lead frame providing electrical connection to external circuitry.
Packaging has advanced beyond using only a lead frame for connecting the integrated circuitry on the die to external circuitry. Packaging called direct chip attach (DCA) has a lead frame that has a lead that contacts one surface of the die and uses conductive solder bumps formed directly on the opposite die surface as other leads.
One of the disadvantages associated with DCA is the additional manufacturing steps needed to form an under barrier metal structure on the die metallization to prevent solder from contaminating the die.
External connections to the die and lead frame of DCA packages typically are made with solder bumps. Where a DCA device requires a connection to the die's back surface, the leadframe is bent so that the lead frame bumps are formed in nearly in same plane as the die bumps in order to ensure that all leads uniformly contact a system circuit board. However, previous DCA devices suffer from as low yield due to misalignment of the die to the lead frame, which results in the lead frame bumps and die bumps being misaligned with respect to each other. Even if a die is placed perfectly on the leadframe, misalignment may occur when a die attach material such as solder is reflowed because the die can “float” out of alignment with the leadframe. The misalignment reduces the process yield and increases the cost of the DCA devices.
Hence, there is a need in the industry for a semiconductor device and method of improving yield in a DCA package in order to reduce the fabrication cost of the device.